Bicomponent fibers are, in and of themselves, well known and have been used extensively to achieve various fiber properties. For example, bicomponent fibers have been formed of two dissimilar polymers so as to impart self-crimping properties. See, U.S. Pat. No. 3,718,534 to Okamoto et al and U.S. Pat. No. 4,439,487 to Jennings. Bicomponent fibers of two materials having disparate melting points for forming point bonded nonwovens are known, for example, from U.S. Pat. No. 4,732,809 to Harris et al. Asymmetric nylon-nylon sheath-core bicomponent fibers are known from U.S. Pat. No. 4,069,363 to Seagraves et al.
The particular cross-sectional geometry of synthetic fibers is also well known to affect certain physical properties. For example, yarns formed of trilobal cross-section fibers have been used extensively as carpet face fibers. Fibers of virtually any cross-sectional geometry are formed by melt-spinning fiber-forming polymers though specially designed spinnerets. That is, in order to achieve fibers of a specific cross-sectional geometry, a corresponding spinneret orifice of specific geometric design is typically needed. Therefore, the present state of this art requires that different spinnerets be provided for each different cross-sectional fiber geometry that is desired to be melt-spun. Spinnerets dedicated to only a single cross-sectional geometry clearly mitigate against processing flexibility since, in order to change a particular spinning line from the production of one fiber cross-section to the production of a different fiber cross-section, the entire spinning line must be shut down to allow for physical installation of a spinnerets dedicated to the new fiber cross-section.
It would therefore be highly desirable if a process could be provided whereby a single spinneret design would be capable of forming fibers of various desired cross-sectional geometries. It is toward fulfilling such a need that the present invention is directed.
Broadly, according to the present invention, bicomponent fibers of different cross-sections may be formed without changing the geometry of the spinneret orifices. More specifically, according to the present invention, at least two polymers are co-melt-spun through an orifice of fixed geometry so as to achieve a bicomponent fiber having a desired cross-section. In order to change to a bicomponent fiber having a cross-section which is different, therefore, at least one of (1) the differential relative viscosity between the first and second polymers, (2) the relative proportions of the first and/or second polymers, and (3) the cross-sectional bicomponent distribution of the first and second polymers, is changed. In such a manner, therefore, a wide variety of bicomponent fibers having different cross-sectional geometries may be produced without changing the fixed geometry orifice through which the polymers are co-melt-spun. Thus, bicomponent fiber cross-sections may be "engineered" to suit a variety of needs without necessarily shutting down production fiber-spinning equipment in order to change spinnerets.
Further aspects and advantages of this invention will become more clear from the following detailed description of the preferred exemplary embodiments.